iTALC is a free classroom management software which enables teachers to view and control computers in their labs and interact with students. It supports Linux and Windows XP (Vista/7 soon) and it even can be used in mixed environments transparently.

Zenoss Core is today's premier, open-source IT monitoring solution. Using a single, web-based console and agentless technology, you can monitor and manage the performance and availability of all devices in your IT infrastructure (network, server, storage, applications, converged infrastructure, virtualization/cloud).
The power of Zenoss Core begins with its in-depth IT inventory and configuration database. Zenoss creates this database by discovering managed resources -- networks, servers, storage, and other devices -- in your IT environment.
Once Zenoss Core discovers the IT infrastructure, it automatically begins monitoring the performance of each device and provides event and fault management capabilities. These capabilities help drive IT operational efficiency and productivity by automating many of the monitoring, notification, alert, escalation, and remediation tasks you perform each day.

Efficient Client-Server Backup system for Linux and Windows. A client for Windows lets you backup open files and complete partition images. Backups are stored to disks in a efficient way (deduplication) on either Windows or Linux servers.

Ettercap is a multipurpose sniffer/interceptor/logger for switched LAN.
It supports active and passive dissection of many protocols (even ciphered ones) and includes many feature for network and host analysis. Development has been moved to GitHub, https://github.com/Ettercap/ettercap

NSClient++ is a windows service that allows performance metrics to be gathered by Nagios (and possibly other monitoring tools). It is an attempt to create a NSClient and NRPE compatible but yet extendable performance service for windows.